In a before and after trial involving 43 healthy adults the investigators measured the effect of six months of supervised exercise on the spontaneous and phytohemagglutinin-induced production of osteoclastogenic cytokines (interleukin-1α, tumor necrosis factor-α), anti-osteoclastogenic cytokines (transforming growth factor-β, interleukins 4 and10), pleiotropic cytokines with variable effects on osteoclastogenesis (interferon-γ, interleukin-6), and T cell growth and differentiation factors (interleukins 2 and 12) by peripheral blood mononuclear cells. The investigators also measured lymphocyte phenotypes, and serum markers of bone formation (osteocalcin), bone resorption (C-terminal telopeptides of Type I collagen), and bone homeostasis (estradiol, vitamin D2, testosterone, parathyroid hormone, insulin-like growth factor).